OBJECTIVE0 An evaluation of functional, metabolic and morphologic effects of (1) osmotically balanced solutions with high potassium concentrations and (2) hyperosmolar mannitol solution during anoxic cardiac arrest and total circulatory arrest. These agents could provide a means of extending tolerable period of cardiac and cerebral ischemia during clinical openheart surgery with or without total circulatory arrest. METHODS: Isolated canine heart preparation will be subjected to varying period of ischemic arrest. Functional, metabolic and morphologic changes of the myocardium will be evaluated by measurements of left ventricular performance depletion-regeneration rates of glycogen and high energy phosphates, cytochemical and histological examinations of serial biopsies of the left ventricle, and the rate of accumulation of intramyocardial carbon dioxide. Comparison will be made in hearts which had or had not been pre-treated with either hyperkalemic or hyperosmolar mannitol solution prior to ischemic arrest. These studies will be then extended to intact dogs subjected to normothermic ischemic arrest during total cardiopulmonary bypass. Both immedate and late (3 - 6 months) effects on myocardial function and structure will be studied. If these studies prove to be beneficial, their effects on cerebral function, metabolism and structure during periods of total circulatory arrest will be analysed.